In many contexts, before a craftsperson can apply casing to windows and/or doors, he or she must set a reveal width and mark that reveal width on the jambs for the windows and/or doors to which the casing is to be applied. The reveal width is the distance from the interior surface of the jambs to the interior surface of the casing. In the United States, typical reveal widths are ⅛ in. (0.3175 cm), ¼ in. (0.635 cm), and ⅜ in. (0.9525 cm), though other reveal widths are clearly possible. In other parts of the world, the typical reveal widths likely differ from those in the United States.
To mark reveal widths, craftspeople often use a standard tape measure and a pencil. They hold the tape measure at the interior surface of the jamb and measure outwardly to the predetermined reveal width. They then draw a free-hand line with their pencils on the door jamb to indicate the reveal width. They typically repeat this process of marking reveal widths eight times per window/door—twice on each of the four jambs, often at or near the corners.
Only after the reveal widths are marked do craftspeople typically attach the casing. They often position the casing such that the interior surface of the casing is aligned with the reveal marks on the jambs and the interior points of the mitered edges are aligned with the corners. Once positioned, the casing can be fastened to the jambs (e.g., by finishing nails).
The process of marking reveal widths can be cumbersome and/or time-consuming. Aligning the tape measure eight times per window/door can be time consuming. This is especially so because craftspeople often do not use the end of the tape measures due to inaccuracies that result from the tab becoming loose. Instead, craftspeople often align the 1 in. marker of a common American tape measure with the interior surface of the jambs and measure the reveal width to, e.g., 1⅛ in. Aligning the 1 in. marker with the interior surface of the jambs can consume valuable time. Moreover, to perform the alignment, and to mark the reveal width, the craftsperson needs to be able to see the tape measure, so he or she must be at eye level with the tape measure. To do so for the top jamb on many windows and doors, he or she must use, e.g., a ladder. Positioning and re-positioning ladders can be cumbersome and time consuming.
Tools other than tape measures can also assist in marking reveal widths. For example, an adjustable tri-square can be used. Adjustable tri-squares, however, tend to be rather large and bulky. Carrying them in one's pocket or tool belt can be difficult, if not impossible. Furthermore, in order to mark all of the reveal widths on the window/door, a craftsperson must still make eight marks with the adjustable tri-square, meaning that the adjustable tri-square must be turned both ways at each corner. Moreover, with each turn, the adjustable tri-squares must be reset for the new orientation. Additionally, due to the difficulty of getting the adjustable tri-square into the corner of the jambs, pencil marks typically have to be relatively long. Long pencil marks can be problematic, given that pencil marks can show on the finished windows/doors in the absence of a dark finishing stain.
Marking reveal widths according to the methods described above can also lead to inaccuracies. Mis-aligning the tape measure, mis-reading the tape measure, and mis-marking distances can all lead to inaccurately marked reveal widths. Using adjustable tri-squares can also lead to inaccuracies. Moreover, using the tape measure as described above often involves free-hand line drawing, which can often lead to inaccuracies. Furthermore, small inaccuracies in reveal width markings can have a significant detriment to the appearance of the casing. In other words, the two casing pieces that meet in a corner may not be oriented perpendicularly to each other, which would prevent their mitered edges from fitting together snugly.
Guarding against the difficulties associated with the above-discussed methods for marking reveal widths often requires a more experienced craftsperson to perform the task of marking the reveal widths. Marking accurately and efficiently is often a skill that is developed through experience. When such an experienced craftsperson is required to mark reveal widths, he or she is likely unable to simultaneously perform other tasks.